You recognize this as a Host Devil. Other than the standard traits of devils, you know that all Host Devils in a wide radius share senses continually. You've also heard that they have some sort of nauseating / debilitating stench, or possibly a breath attack.

If possible then Azatoth will move forward to confront and attack the birdman in melee to make it harder for him to utilize ranged attacks or magic. If he cannot reach the man and do an attack he will still make a run to the birdman to cover the group.

Round 1
Hadassah -- moves up, casts Evil Eye
Moulini -- still out in the main room, draws her rapier, calls out
Shel -- still out in the draws and loads her sling
Gryne -- moves up, shoots, misses
James -- moves up, shoots, hits

The creature beats its wings twice, and glides over the gaping hole in the floor. It floats up to D1, diagonal from James, and sends some telepathic message inexpressible in words, but filled with hate and anticipation.
Attack:1d20 + 9 ⇒ (13) + 9 = 22 -- it strikes, for 1d8 + 1 ⇒ (4) + 1 = 5 points of damage.
At the same time, it attempts to grapple James' wrist with one of its talons: CMB:1d20 + 4 ⇒ (3) + 4 = 7, but is unable to gain purchase.

Azatoth moves from A2 to C1 and attacks the monster. 1d20 + 4 ⇒ (3) + 4 = 7: His scimitar has a cleam shot for the creature's neck, but it manages to interpose the shaft of its spear. Even with Hadassah's curse, the creature manages to block Azatoth's blow.

Maximo, you're up. Did you still want to cast detect evil, or are you willling to go with a natural assumption?

I was hoping to keep it talking long enough to slip in the detect evil before combat. But, now that we've jumped the gun, literally, let's just go with the assumption.

I am Maximo Interresante, blessed knight of Shelyn! Maximo thunders. If you can still speak telepathically without a head, then your remains can tell the next mortal, immortal, or bad smell that passes by, who it was that brought you low!

Dropping shield and mace, then slowly drawing his antique greatsword as he closes to melee, he kisses the hilt and calls upon Shelyn's divine power to help him smite the creature, then attacks with all his might.

Maximo, the creature is in D1. Your best bet for getting next to it is to move from A1 to B2 (moving through Hadassah), to C2 (moving through James) to D2, and attacking from there. That would allow it an attack of opportunity against you as you move from C2 to D2. On the other hand, if you have smite evil up, your AC may be good enough that it wouldn't be able to hit you.

You have enough movement to continue moving to E1 if you wanted to do so. That would set up a flank with Azatoth. The obvious danger there is that the monster might try to bul rush you 5 feet and send you falling out the crevase in the floor.

I will accept the AoO if it's the only way to get to melee. However, I thought James was trying to step away? If possible, I'll try to get both James and Hadassah to shuffle back, then I should be able to take James' spot. If that means I go later in the round that's ok, since I'll still go before chicken-boy.

Make way, make way! Maximo bellows, trying to wade forward through his companions. It must be happy hour at the Happy Harpy. Hadassah! James! Withdraw so that I may sally forth!

If possible, I will maintain line of sight to the demon, otherwise, she retreats as soon as she completes her curse. The link you sent to the demon does not show any information on the demon, it just shows me the cover of the AP.

Hadassah feels the universe sigh as the first Evil Eye releases, and she casts another. The monster attempts to resist:1d20 ⇒ 3, but gets ensnared in her powers. She then steps back to A2, right next to the door into the very warm building.

The blade sinks into the monster's shoulder, almost severing its head.

So! The pure ones have sent a minion. Very well. Let your death serve as a warning to the dogs of Sarenrae, that illegal trespass here shall be answered. As will your sword blow.

Moulini moves into the room, at A1, pleading with the creature. She hears a voice in the back of her mind, like honey-covered rage and hate.

Moulini:

I see that these raiders have taken you as one of them. It would be easy for you to continue the charade, petitioner, and stay in the corner, apart from the fight. But Moloch does not need mewling cowards in his forces. Here is where you must make a choice. Foul the armored one's weapon, or wrest it from his grasp. Make it seem like an accident, if you would keep your cover a little longer. I shall take the others. Do this, and I will spare the life of one of these, so that she might spread the word of Moloch's return.

Gryne, you stop momentarily to look at the fantastic stonework in the corridor.
Perception:1d20 + 10 ⇒ (14) + 10 = 24; it looks like it was carved from a single piece of stone, hollowed out and sculpted like an inside-out statue. The gigantic, hideous faces along the walls serve as windows, with openings in their eyes and mouths allowing the desert air to pass through. And that's probably what caused all the damage here. Unlike the building that you've been in, which has been buried under the Qadiran desert for centuries, this bridge has allowed sand to pass through.

Azatoth attack, and, seeing that Gryne is planning to fire, steps out of his way.
Attack:1d20 + 5 ⇒ (15) + 5 = 20; a hit!
Damage:1d6 + 3 ⇒ (3) + 3 = 6 points. As with James' bullet, it looks like something about the creature is turning a good blow into nothing more than a small cut.
Azatoth then steps from C1 to D2, between Maximo and the chasm, opening a line of fire for Gryne.

Gryne fires a second arrow, just as he gets a clear shot at the monster.
Attack:1d20 + 4 ⇒ (18) + 4 = 22, -4 for firing into melee, a hit!
Damage:1d8 + 2 ⇒ (6) + 2 = 8, a shot straight into the monster's chest. It swings its head towards you for a moment and puls the arrow out. Immediately, the wound closes, leaving only a minor cut.

The monster swivels its head to Azatoth. Sink to your knees, beast, at the stentch of Hell. It breathes deeply and blows a cloud of orange gas at Azatoth.
Fort:1d20 + 4 ⇒ (4) + 4 = 8 -- Azatoth is sickened, his eyes losing focus and his knees bucking momentarily.

Its gaze then returns to James. You seek to flee, mortal, to save your wretched blink of life? It is hopeless. I shall pursue you till you tire and fall. And if I fail, all the Gaav know to pursue you. You are hunted. You shall never know rest while you draw breath.

It moves to E2, directly east of Azatoth. It's hovering above the gap in the floor, as if it's daring anybody to approach.

Moulini, it moved to E2, so it's no longer next to Maximo. You could move to F2, if you wanted to flank it with Azatoth. That would involve dodging its attack of opportunity as you moved around it, and also jumping the rift in the floor of the tunnel, so there's some risk involved, but it's possible. Is that what you want to do?

Hadassah moves as if to draw her crossbow, then hesitates, realizing that if the mysterious pistol is unable to damage the odd creature, her crossbow has little to now chance. Instead she holds her action, waiting for a more opportune moment to act.

At Shel's urging, Gryne loads one of the arrows found on the bodies of the Sarenrae cultists outside the temple. As he draws the string, he can feel, just for an instant, one of the ancient dead alongside him, pulling the arrow back with him. He aims, relaxes, and lets the arrow fly.

Attack:1d20 + 5 ⇒ (11) + 5 = 16 - 4 for firing into melee = 12.

The arrow strikes the floor, just at the crevasse, and ricochets up below the creature's feet. Even though you missed, the monster looks at you, its posture betraying some of its alarm.

There's a 50% chance that ammunition that misses is destroyed or otherwise broken, and that applies to magical ammunition as well. The arrow is on the other side of the room, near the giant brass face. It's not lost, but someone will need to examine it to judge wether it's taken enough damage to render it unusable

If Gaav attacks and hits a party member, causing them to lose 50% or more of their health, my action is to move and cast Cure Light Wounds on the injured party member, avoiding all Attacks of Opportunity.

If this does not happen, I will hold action until after all companions have acted, then hex Gaav's Saves.

I will enlighten my companions as to the weaknesses and strengths of Gaav as I understand them, but I cannot follow the link in your post.

Sorry for the very OOC nature of this, but I may not be available once Moulini posts, and I don't want the entire combat stopped while you wait for me to take my action. Any major "WTF?!?" moments may change my plan if they occur before I act. If such a moment occurs and I do not reply promptly, feel free to assume Hadassah is temporarily wrapped up in combat and failed to notice the event.

Hadassah notes: "The 'Porter' here is a Gaav, one of the minor devils. (So, like all devils, it's immune to fire and poison.) Acid attacks and cold attacks don't work well, either, and we'll need good aligned weapons to do it real damage. I don't think this kind of devil heals quickly, however.

"The Gaav come in large packs, and whatever this one sees or hears, all the others within a couple days' travel will also know. They've got some magic powers, but that's mostly designed to fool people. Illusions, phantom sounds, that sort of stuff. And they have really bad breath."

Hadassah turns toward James and speaks: "The flame of life burns hot and bright, to strengthen people through the night. The holy fire brings you weal; it asks your body now to heal." And with that, James gains 1d8 + 1 ⇒ (5) + 1 = 6 hit points, healing completely.

Mourini moves to C2, threatening Maximo with her rapier. "Drop your weapon, Maximo. I need the Porter, alive, and I'll strike down anyone who tries to kill him."

The Porter laughs at this, but chooses to glide back to F2, and cast a spell. He vanishes from sight...

Shel:

... to appear 10' south of Shel.

Position check. Shel is in the hot room, behind the throne in the shape of a hand of flame. She hasn't yet gone through the door she opened.Hadassah is right next to Shel, just on the other side of the door, in A2.Gryne is in B1. James is in B2.Molini has just moved to C2.Maximo is in D1. Azatoth is in D2.

Giving Moulini a double-take, Maximo calls over his shoulder. I apologize, my lady, but if there is one talent I lack, it is bargaining with hellish creatures dedicated to evil devil-gods! I will assume some foul magic has caused you to level your blade at me, and so will not take offense. However, since I can't have you poking at my backside. Eying Gryne and James, he suggests in a commanding voice. You two! Would you do me the favor of escorting the lady Moulini into a fifty foot rope while I finish my business with the Porter?

Turning back to the devil, he nearly curses in front of the ladies before catching himself. By Shelyn's massive t... err.. hrmmph. Stand and fight, creature!